Phosphatidylinositol 3-kinase is essential for kit ligand-mediated survival, whereas interleukin-3 and flt3 ligand induce expression of antiapoptotic Bcl-2 family genes

Cardiac Mast Cells: A Two-Head Regulator in Cardiac Homeostasis and Pathogenesis Following Injury

Cardiac mast cells (CMCs) are multifarious immune cells with complex roles both in cardiac physiological and pathological conditions, especially in cardiac fibrosis. Little is known about the physiological importance of CMCs in cardiac homeostasis and inflammatory process. Therefore, the present review will summarize the recent progress of CMCs on origin, development and replenishment in the heart, including their effects on cardiac development, function and ageing under physiological conditions as well as the roles of CMCs in inflammatory progression and resolution. The present review will shed a light on scientists to understand cardioimmunology and to develop immune treatments targeting on CMCs following cardiac injury.

Noncanonical Cell Fate Regulation by Bcl-2 Proteins

Bcl-2 proteins are widely known as key controllers of mitochondrial outer membrane permeabilization, arguably the most important step of intrinsic apoptosis. Accumulating evidence indicate that most, if not all, members of the Bcl-2 protein family also mediate a number of apoptosis-unrelated functions. Intriguingly, many of these functions ultimately impinge on cell fate decisions via apoptosis-dependent or -independent mechanisms, delineating a complex network through which Bcl-2 family members regulate cell survival and death. Here, we critically discuss the mechanisms through which Bcl-2 proteins influence cell fate as they regulate autophagy, cellular senescence, inflammation, bioenergetic metabolism, Ca²⁺ fluxes, and redox homeostasis.

Stemness of T cells and the hematopoietic stem cells: fate, memory, niche, cytokines

Stem cells are able to generate both cells that differentiate and cells that remain undifferentiated but potentially have the same developmental program. The prolonged duration of the protective immune memory for infectious diseases such as polio, small pox, and measles, suggested that memory T cells may have stem cell properties. Understanding the molecular basis for the life-long persistence of memory T cells may be useful to project targeted therapies for immune deficiencies and infectious diseases and to formulate vaccines. In the last decade evidence from different laboratories shows that memory T cells may share self-renewal pathways with bone marrow hematopoietic stem cells. In stem cells the intrinsic self-renewal activity, which depends on gene expression, is known to be modulated by extrinsic signals from the environment that may be tissue specific. These extrinsic signals for stemness of memory T cells include cytokines such as IL-7 and IL-15 and there are other cytokine signals for maintaining the cytokine signature (TH1, TH2, etc.) of memory T cells. Intrinsic and extrinsic pathways that might be common to bone marrow hematopoietic stem cells and memory T lymphocytes are discussed and related to self-renewal functions.

TNF-α/Fas-RIP-1-induced cell death signaling separates murine hematopoietic stem cells/progenitors into 2 distinct populations

We studied the effects of TNF-α and Fas-induced death signaling in hematopoietic stem and progenitor cells (HSPCs) by examining their contributions to the development of bone marrow failure syndromes in Tak1-knockout mice (Tak1(-/-)). We found that complete inactivation of TNF-α signaling by deleting both of its receptors, 1 and 2 (Tnfr1(-/-)r2(-/-)), can prevent the death of 30% to 40% of Tak1(-/-) HSPCs and partially repress the bone marrow failure phenotype of Tak1(-/-) mice. Fas deletion can prevent the death of 5% to 10% of Tak1(-/-) HSPCs but fails to further improve the survival of Tak1(-/-)Tnfr1(-/-)r2(-/-) HSPCs, suggesting that Fas might induce death within a subset of TNF-α-sensitive HSPCs. This TNF-α/Fas-induced cell death is a type of receptor-interacting protein-1 (RIP-1)-dependent programmed necrosis called necroptosis, which can be prevented by necrostatin-1, a specific RIP-1 inhibitor. In addition, we found that the remaining Tak1(-/-) HSPCs died of apoptosis mediated by the caspase-8-dependent extrinsic apoptotic pathway. This apoptosis can be converted into necroptosis by the inhibition of caspase-8 and prevented by inhibiting both caspase-8 and RIP-1 activities. We concluded that HSPCs are heterogeneous populations in response to death signaling stimulation. Tak1 mediates a critical survival signal, which protects against both TNF-α/Fas-RIP-1-dependent necroptosis and TNF-α/Fas-independent apoptosis in HSPCs.

Bcl-2 expression and apoptosis in the regulation of hematopoietic stem cells

Apoptosis or programmed cell death plays a pivotal role in regulating tissue homeostasis in the adult and in tissue remodeling during embryogenesis. As in other tissues, apoptosis plays an important role within the hematopoietic system in removing aged and non-functional cells. It plays a particularly important role in regulating the cells of the immune system. The signals and molecules regulating apoptosis in these immune cells have been intensely investigated over the years, providing great insight into the mechanisms involved. In contrast, much less is known about the regulation and role of apoptosis in the cells that produce differentiated hematopoietic cells, namely the hematopoietic stem cells (HSCs). It is appreciated that HSCs are under tight regulatory control, as either excessive proliferation or apoptosis will result in too many or too few hematopoietic cells (for example, leukemia or anemia). Apoptosis thus plays an essential role in maintaining the appropriate balance of HSC and mature blood cells and in protecting the HSC pool for life-long hematopoiesis. This review summarizes the current knowledge concerning apoptosis and its role in the physiology of the hematopoietic system, especially within the HSC compartment.

Mitf dosage as a primary determinant of melanocyte survival after ultraviolet irradiation

Microphthalmia-associated transcription factor (Mitf) is essential for melanocyte development and function and regulates anti-apoptotic Bcl2 expression. We hypothesized that cellular deficiency of Mitf can influence melanocyte survival in response to ultraviolet (UV) radiation. Primary melanocyte cultures were prepared from neonatal wild-type mice and congenic animals heterozygous for Mitf mutations Mitf (mi-vga9/+) and Mitf(Mi-wh/+) and exposed to UV irradiation. Wild-type melanocytes were more resistant to UV-induced apoptosis than melanocytes partially deficient in Mitf activity, as determined by relative levels of intracellular melanin and relative activation of Mitf target genes Tyr, Tyrp1, Dct, and Cdk2. Comparative experiments with wild-type cells and congenic albino melanocytes demonstrated that these differences are not due to differences in melanin content, implicating Mitf as a primary determinant of UV-dependent melanocyte survival. Mitf activity correlated directly with resistance to UV-induced apoptosis in melanocytes. Mitf was important not only for regulating the expression of anti-apoptotic Bcl-2 following UV irradiation, but also the expression of the pro-apoptotic BH3-only Bad protein and activation of the extrinsic apoptotic pathway. Hence, Mitf is a multifaceted regulator of UV-induced apoptosis in melanocytes.

Bcl-2 and Bcl-XL are indispensable for the late phase of mast cell development from mouse embryonic stem cells

OBJECTIVE

The aim of this study was to determine the importance of the prosurvival factors Bcl-2 and Bcl-XL for mast cell development and survival.

METHODS

bcl-x(-/-) and bcl-2(-/-) mouse embryonic stem cells were maintained in medium supplemented with either interleukin (IL)-3 or IL-3 in combination with stem cell factor (SCF) to favor mast cell development. The development of Bcl-2 family deficient embryonic stem cell-derived mast cells (ESMCs) was monitored and Bcl-2 family gene expression and cell numbers were analyzed.

RESULTS

Deficiency in either bcl-x or bcl-2 totally inhibited the development of ESMCs when IL-3 alone was used as a mast cell growth factor. Intriguingly, when IL-3 was used in combination with SCF, the ESMCs developed normally the first 2 weeks but thereafter the cell numbers dropped drastically. The remaining ESMCs express mouse mast cell protease 1, suggesting a mucosal-like phenotype. ESMCs lacking bcl-x or bcl-2 exhibited strong expression of A1, another prosurvival Bcl-2 family member.

CONCLUSION

For the first time we provide direct evidence that both bcl-x and bcl-2 are indispensable for mast cell survival during the late phase of their development.

Early myeloid cells expressing c-KIT isoforms differ in signal transduction, survival and chemotactic responses to Stem Cell Factor

Isoforms of the receptor tyrosine kinase, c-KIT, differ in the presence or absence of a GNNK tetrapeptide in the extracellular juxtamembrane region. When expressed in murine NIH3T3 cells, these isoforms of c-KIT showed differential activation of signaling pathways and proliferation in response to Stem Cell Factor (SCF). However, c-KIT is not normally expressed by fibroblasts, but plays a key role in hematopoiesis. Because signaling pathways and cellular responses mediated by c-KIT differ in different cell types, we studied the effects of SCF stimulation on factor-dependent murine early myeloid cells expressing human GNNK+ or GNNK- c-KIT. As in fibroblasts, SCF activation of the GNNK- isoform resulted in stronger, more rapid receptor phosphorylation, and activation of Src kinases, while only a minor effect on the phosphatidylinositol 3-kinase pathway was observed. Similarly, more rapid Src kinase-dependent internalisation of the GNNK- isoform occurred in response to SCF. In contrast to fibroblasts, only minor differences in ERK activation were seen indicating that early hematopoietic cells, unlike fibroblasts, are not dependent on Src kinases for activation of this pathway in response to SCF. Enhanced SCF-dependent growth was observed in GNNK- c-KIT expressing cells due to lower cell attrition. The rate of cell division was similar. Importantly, cells expressing the GNNK- isoform showed a greater chemotactic response to SCF.

Bcl11b mutations identified in murine lymphomas increase the proliferation rate of hematopoietic progenitor cells

BACKGROUND

The telomeric region of mouse chromosome 12 has previously shown frequent allelic loss in murine lymphoma. The Bcl11b gene has been identified and suggested as a candidate tumor suppressor gene within this region. In this study, we aimed to elucidate whether Bcl11b is mutated in lymphomas with allelic loss, and whether the mutations we detected conferred any effect on cell proliferation and apoptosis.

METHODS

Mouse lymphomas induced by 1,3-butadiene or 2',3'-dideoxycytidine were analysed for mutations in the Bcl11b gene using single strand conformation analysis and direct DNA sequencing. Effects on cell proliferation by the detected mutations were studied by expressing wild-type and mutant Bcl11b in the cytokine-dependent hematopoietic progenitor cell line FDC-P1, lacking endogenous Bcl11b expression.

RESULTS

Missense and frameshift (FS) mutations were identified in 7 of 47 tumors (15%). Interestingly, all mutations were found between amino acids 778-844 which encode the three C-terminal DNA-binding zinc fingers. In FDC-P1 cells, wild-type Bcl11b suppressed cell proliferation, whereas the mutated versions (S778N, K828T, Y844C and FS823) enhanced proliferation several-fold.

CONCLUSION

The genetic alterations detected in this study suggest that the three C-terminal zinc fingers of Bcl11b are important for the DNA-binding. Cell proliferation was suppressed by overexpression of wild-type Bcl11b but enhanced by mutant Bcl11b, indicating that these mutations may be an important contributing factor to lymphomagenesis in a subset of tumors.

Constitutively activated FLT3 phosphorylates BAD partially through pim-1

Constitutively activating internal tandem duplication (ITD) mutations of the receptor tyrosine kinase FLT3 (Fms-like tyrosine kinase 3) play an important role in leukaemogenesis and their presence is associated with a poor prognosis in acute myeloid leukaemia (AML). Examining the anti- and proapoptotic proteins in constitutively activated FLT3 signalling in BaF3/ITD and MV4-11 cells, we found that the level of Bcl-2 antagonist of cell death (BAD) phosphorylation was greatly decreased in response to FLT3 inhibition. Both Ser-112 and Ser-136 of BAD are rapidly dephosphorylated after treatment with the FLT3 inhibitor CEP-701 in BaF3/ITD and MV4-11 cells. In confirmation of the cell line data, BAD was highly phosphorylated in both constitutively activated wild-type and mutant FLT3 primary AML samples, and rapidly dephosphorylated after treatment of the primary samples with CEP-701. Upstream proteins known to phosphorylate BAD include Akt, extracellular signal-regulated kinase/mitogen-activated protein kinase (Erk/ MAPK), Pim-1 and Pim-2. We and other groups have shown that constitutively activated FLT3 induces multiple signalling pathways, including phosphatidylinositol 3-kinase (PI3K)/Akt, Erk/MAPK and Janus kinase/signal transducers and activators of transcription (Jak/STAT). Thus, BAD may be a nexus point upon which these multiple signalling pathways converge in FLT3-mediated cell survival. In support of this, siRNA knockdown of BAD expression in MV4-11 cells conferred resistance to CEP-701-mediated apoptosis. Our data suggests that Pim-1 is one of the principal kinases mediating the anti-apoptotic function of FLT3/ITD signalling via the phosphorylation of BAD.

Flt3 Y591 duplication and Bcl-2 overexpression are detected in acute myeloid leukemia cells with high levels of phosphorylated wild-type p53

Loss or mutation of the TP53 tumor suppressor gene is not commonly observed in acute myeloid leukemia (AML), suggesting that there is an alternate route for cell transformation. We investigated the hypothesis that previously observed Bcl-2 family member overexpression suppresses wild-type p53 activity in AML. We demonstrate that wild-type p53 protein is expressed in primary leukemic blasts from patients with de novo AML using 2-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and phospho-specific flow cytometry. We found that p53 was heterogeneously expressed and phosphorylated in AML patient samples and could accumulate following DNA damage. Overexpression of antiapoptosis protein Bcl-2 in AML cells was directly correlated with p53 expression and phosphorylation on serine residues 15, 46, and 392. Within those patients with the highest levels of Bcl-2 expression, we identified a mutation in FLT3 that duplicated phosphorylation site Y591. The presence of this mutation correlated with greater than normal Bcl-2 expression and with previously observed profiles of potentiated STAT and MAPK signaling. These results support the hypothesis that Flt3-mediated signaling in AML enables accumulation of Bcl-2 and maintains a downstream block to p53 pathway apoptosis. Bcl-2 inhibition might therefore improve the efficacy of existing AML therapies by inactivating this suppression of wild-type p53 activity.

KIT/KIT Ligand in Mammalian Oogenesis and Folliculogenesis: Roles in Rabbit and Murine Ovarian Follicle Activation and Oocyte Growth1

In rodent ovaries Kit ligand (KITL) and its receptor KIT have diverse roles, including the promotion of primordial follicle activation, oocyte growth, and follicle survival. Studies were undertaken to determine whether KITL and KIT carry out similar activities in rabbits. KitlandKitmRNA and protein were localized to oocytes and granulosa cells, respectively, in the rabbit ovary. Ovarian cortical explants from juvenile rabbits and neonatal mouse ovaries were subsequently cultured with recombinant mouse KITL and/or KITL neutralizing antibody. Indices of follicle growth initiation were compared with controls and between treatment groups for each species. Recombinant mouse KITL had no stimulatory effect on primordial follicle recruitment in cultured rabbit ovarian explants. However, the mean diameter of oocytes from primordial, early primary, primary, and growing primary follicles increased significantly in recombinant mouse KITL-treated explants compared with untreated tissues. In contrast, recombinant mouse KITL promoted both primordial follicle activation and an increase in the diameter of oocytes from primordial and early primary follicles in the mouse, and these effects were inhibited by coculture with KITL-neutralizing antibody. Recombinant mouse KITL had no effect on follicle survival for either species. These data demonstrate that KITL promotes the growth of rabbit and mouse oocytes and stimulates primordial follicle activation in the mouse but not in the rabbit. We propose that the physiologic roles of KITL and KIT may differ between species, and this has important implications for the design of in vitro culture systems for folliculogenesis in mammals, including the human.

FLT-3: a new focus in the understanding of acute leukemia

The FMS-like tyrosine kinase-3 (FLT-3), which belongs to the class III receptor tyrosine kinase family, is primarily expressed by hematopoietic cells and plays an important role in hematopoiesis. FLT-3 is also expressed in the majority of acute leukemias, in which the presence of FLT-3 activating mutations is associated with poor prognosis. Consequently, there has been a recent surge in the development of FLT-3 inhibitors for the molecular targeting of leukemia, and many of these are now in clinical trials. An improved understanding of how FLT-3 interacts with its ligand, as well as how FLT-3 activating mutations are able to trigger downstream intracellular signaling pathways, will provide greater insight to how small molecule inhibitors may best be utilized and combined with established chemotherapeutic drugs for the management of patients with high-risk acute leukemia.

Stem cell factor promotes mast cell survival via inactivation of FOXO3a-mediated transcriptional induction and MEK-regulated phosphorylation of the proapoptotic protein Bim

Mast cells are found in tissues throughout the body where they play important roles in the regulation of inflammatory responses. One characteristic feature of mast cells is their longevity. Although it is well established that mast cell survival is dependent on stem cell factor (SCF), it has not been described how this process is regulated. Herein, we report that SCF promotes mast cell survival through inactivation of the Forkhead transcription factor FOXO3a (forkhead box, class O3A) and down-regulation and phosphorylation of its target Bim (Bcl-2 [B-cell lymphoma-2] interacting modulator of cell death), a Bcl-2 homology 3 (BH3)-only proapoptotic protein. SCF induced a rapid and transient phosphorylation of Akt (protein kinase B) and FOXO3a. SCF treatment prevented up-regulation of Bim protein expression and led to increased Bim phosphorylation. Bim phosphorylation was inhibited by PD98059 and LY294002 treatment, suggesting the involvement of mitogen-activated protein kinase kinase/mitogen-activated protein kinase (MEK/MAPK) and phosphatidylinositol 3 (PI3)-kinase pathways in this process. Overexpression of phosphorylation-deficient FOXO3a caused an up-regulation of Bim and induced mast cell apoptosis even in the presence of SCF. Mast cell apoptosis induced by the phosphorylation-deficient FOXO3a was attenuated in bim-/- mast cells. Because apoptosis is abnormally reduced in bim-/- mast cells, these data provide evidence that Akt-mediated inhibition of FOXO3a and its transcription target Bim provides an important mechanism by which SCF acts to prevent apoptosis in mast cells.

Transforming growth factor-{beta}1 modulates responses of CD34+ cord blood cells to stromal cell-derived factor-1/CXCL12

Disruption of stromal cell-derived factor-1 (SDF-1/CXCL12 [CXC chemokine ligand 12]) interaction leads to mobilization of stem/progenitor cells from bone marrow to circulation. However, prolonged exposure of CD34+ cells to SDF-1 desensitizes them to SDF-1. So how do cells remain responsive to SDF-1 in vivo when they are continuously exposed to SDF-1? We hypothesized that one or more mechanisms mediated by cytokines exist that could modulate SDF-1 responsiveness of CD34+ cells and the desensitization process. We considered transforming growth factor-beta1 (TGF-beta1) a possible candidate, since TGF-beta1 has effects on CD34+ cells and is produced by stromal cells, which provide niches for maintenance and proliferation of stem/progenitor cells. TGF-beta1 significantly restored SDF-1-induced chemotaxis and sustained adhesion responses in cord blood CD34+ cells preexposed to SDF-1. Effects of TGF-beta1 were dependent on the dose and duration of TGF-beta1 pretreatment. Phosphorylation of extracellular signal-regulated kinase 1 (Erk1)/Erk2 was implicated in TGF-beta1 modulation of migratory and adhesion responses to SDF-1. Our results indicate that low levels of TGF-beta1 can modulate SDF-1 responsiveness of CD34+ cells and thus may facilitate SDF-1-mediated retention and nurturing of stem/progenitor cells in bone marrow.

Expression of a constitutively active mutant of M-Ras in normal bone marrow is sufficient for induction of a malignant mastocytosis/mast cell leukemia, distinct from the histiocytosis/monocytic leukemia induced by expression of activated H-Ras

Expression of constitutively activated M-Ras in normal murine bone-marrow cells was sufficient to induce the factor-independent, in vitro growth and differentiation of colonies of macrophages and neutrophils, and the generation of immortal lines of factor-independent mast cells, and, upon in vivo injection of the transduced cells, a fatal mastocytosis/mast-cell leukemia. In contrast, expression of constitutively activated H-Ras in bone-marrow cells resulted in the in vitro growth, in the absence of exogenous factors, of colonies that contained only macrophages and of lines of cells resembling dendritic cells, and, upon in vivo injection of the transduced cells, a fatal histiocytosis/monocytic leukemia. Macrophages generated by bone-marrow cells expressing activated M-Ras or activated H-Ras differed morphologically, the latter appearing more activated, a difference abrogated by an inhibitor of Erk activation. Inhibition of either Erk or PI3 kinase blocked the capacity of both activated M-Ras and activated H-Ras to support proliferation and viability. However, inhibition of p38 MAPK activity suppressed proliferation of bone-marrow cells expressing activated H-Ras, but enhanced that of bone-marrow cells expressing activated M-Ras. Thus, expression of either activated M-Ras or H-Ras in normal hematopoietic cells was sufficient for transformation but each resulted in the generation of distinct lineages of cells.

Gene expression profiles at diagnosis in de novo childhood AML patients identify FLT3 mutations with good clinical outcomes

Fms-like tyrosine kinase 3 (FLT3) mutations are associated with unfavorable outcomes in children with acute myeloid leukemia (AML). We used DNA microarrays to identify gene expression profiles related to FLT3 status and outcome in childhood AML. Among 81 diagnostic specimens, 36 had FLT3 mutations (FLT3-MUs), 24 with internal tandem duplications (ITDs) and 12 with activating loop mutations (ALMs). In addition, 8 of 19 specimens from patients with relapses had FLT3-MUs. Predictive analysis of microarrays (PAM) identified genes that differentiated FLT3-ITD from FLT3-ALM and FLT3 wild-type (FLT3-WT) cases. Among the 42 specimens with FLT3-MUs, PAM identified 128 genes that correlated with clinical outcome. Event-free survival (EFS) in FLT3-MU patients with a favorable signature was 45% versus 5% for those with an unfavorable signature (P = .018). Among FLT3-MU specimens, high expression of the RUNX3 gene and low expression of the ATRX gene were associated with inferior outcome. The ratio of RUNX3 to ATRX expression was used to classify FLT3-MU cases into 3 EFS groups: 70%, 37%, and 0% for low, intermediate, and high ratios, respectively (P < .0001). Thus, gene expression profiling identified AML patients with divergent prognoses within the FLT3-MU group, and the RUNX3 to ATRX expression ratio should be a useful prognostic indicator in these patients. (Blood. 2004;104:2646-2654)

Inhibition of HMC-1 mast cell proliferation by vitamin E: involvement of the protein kinase B pathway

The effects of four natural tocopherols on the proliferation and signaling pathways were examined in the human mastocytoma cell line (HMC-1). The four tocopherols inhibited HMC-1 cell proliferation with different potency (delta > alpha = gamma > beta). Growth inhibition correlated with the reduction of PKB (protein kinase B) phosphorylation by the different tocopherols. The reduction of PKB phosphorylation led to a decrease of its activity, as judged from a parallel reduction of GSKalpha/beta phosphorylation. The translocation of PKB to the membrane, as a response to receptor stimulation by NGFbeta, is also prevented by treatment with tocopherols. In the presence of PKC or PP2A inhibitors, the reduction of PKB phosphorylation by tocopherols was still observed, thus excluding the direct involvement of these enzymes. Other pathways, such as the Ras-stimulated ERK1/2 (extracellular signal responsive kinase) pathway, were not affected by tocopherol treatment. The tocopherols did not significantly change oxidative stress in HMC-1 cells, suggesting that the observed effects are not the result of a general reduction of oxidative stress. Thus, the tocopherols interfere with PKB phosphorylation and reduce proliferation of HMC-1 cells, possibly by modulating either phosphatidylinositol 3-kinase, a kinase phosphorylating PKB (PDK1/2), or a phosphatase that dephosphorylates it. Inhibition of proliferation and PKB signaling in HMC-1 cells by vitamin E suggests a role in preventing diseases with mast cell involvement, such as allergies, atherosclerosis, and tumorigenesis.

FLT3 ligand regulates apoptosis through AKT-dependent inactivation of transcription factor FoxO3

Proliferation, differentiation, and survival of hematopoietic cells are regulated by cytokines, acting through specific receptors. FLT3 ligand (FL) is one of the most important cytokines for regulation of the hematopoietic system, and its receptor FLT3 is expressed on both stem cells and progenitors. Regulation of Forkhead transcription factors has been described as an important mechanism to control apoptosis and cell cycle progression in hematopoietic progenitors. Here we report that FL induces AKT/PKB activation, which in turn phosphorylates and thereby inactivates the Forkhead protein FoxO3 in the progenitor cell line FDC-P1 stably expressing murine FLT3 receptor. Phosphorylation of AKT and FoxO3 was blocked by the PI-3 kinase inhibitor LY294002 but not by the MAP kinase inhibitor PD98059. Expression of a mutated FoxO3, in which all three inhibitory phosphorylation sites were mutated to alanine, led to rapid increase of apoptotic cells in the presence of FL. These results suggest that FL-induced regulation of apoptosis is executed by FoxO3.

Interleukin-3 receptor in acute leukemia

Recent studies indicate that abnormalities of the interleukin-3 receptor (IL-3R) are frequently observed in acute myeloid leukemias (AMLs) and may contribute to the proliferative advantage of leukemic blasts. This review analyzes the evidences indicating that the IL-3R represents one of the target molecules involved in the stimulation of proliferation of AMLs, and the overexpression of the IL-3Ralpha chain may represent one of the mechanisms contributing to the development of a highly malignant leukemic phenotype. Furthermore, there is evidence that the IL-3Ralpha is a marker of leukemic stem cells, at variance with normal stem cells that are IL-3Ralpha-. Finally, the IL-3R may represent an important target for the development of new antileukemic drugs.